Process for producing continuous round jacketed lightguides

ABSTRACT

PROCESS AND APPARATUS FOR PROTECTIVELY JACKETING A BUNDLE OF POLYMERIC FILAMENTS BY SIMULTANEOUSLY EXTRUDING A PROTECTIVE JACKET AND CONTACTING THE BUNDLE WITH THE JACKET BEFORE THE JACKET CONTACTS THE EXTRUSION ORIFICE.

Feb. 29, 1972 HAGEF} r 3,646,186

PROCESS FOR PRODUCING CONTINUOUS ROUND JACKETED LIGHTGUIDES Filed June5, 1970 FIG. 3A FIG.A3B FIG.3C $144K, 1/14:

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T nited States Patent Office 3,646,136 Patented Feb. 29, 1972 3,646,186PROCESS FOR PRODUCING CONTINUOUS ROUND JACKETED LIGHTGUIDES Thomas C.Hager, Washington, W. Va., assignor to E. I. du Pout de Nemours andCompany, Wilmington, Del. Continuation-impart of application Ser. No.600,919, Dec. 12, 1966. This application June 5, 1970, Ser. No. 43,701

Int. Cl. B29d 11/00; B29f 3/10; G02b 5/16 US. Cl. 264-174 3 ClaimsABSTRACT OF THE DISCLOSURE Process and apparatus for protectivelyjacketing a bundie of polymeric filaments by simultaneously extruding aprotective jacket and contacting the bundle with the jacket before thejacket contacts the extrusion orifice.

This application is a continuation-in-part of copending application U.S.Ser. No. 600,919, filed Dec. 12, 1966, now abandoned.

This invention relates to the jacketing of continuous plastic opticalfilamentary material to produce a lightguide in which the filamentarymaterial is tightly jacketed and the jacket is round.

Plastic optical filamentary material is defined as being sheathedplastic filaments or fibers which are capable of transmitting light overlong straight or curved lengths. Suitable plastic optical filamentarymaterial that can be used in the practice of this invention is describedin British Pat. No. 1,037,498, entitled Light Transmitting Filaments.The process of this invention can be used to protectively jacket plasticoptical filamentary material of any composition and diameter.

There are two general types of jacketing processes: pressure typeextrusion process and tubing type extrusion process. Both processes havebeen unsuccessful in producing light-guides in which the plastic opticalfilamentary material is satisfactorily tightly jacketed and thejacketing is round.

The most serious problem in jacketing plastic filamentary material isthat many presently available optical filamentary materials are heatsensitive to temperatures above 130 C. In extrusion jacketing processes,the extrudable jacketing material is at a temperature well in excess of130 C. within the extruder. Thus, the jacketing material must not beallowed to remain in prolonged contact with the plastic filaments withinthe extruder or degradation will occur.

In a pressure type extrusion process, the filamentary material issubjected to the high temperatures and pressures of the extrudablematerial for a sufiicient period of time to cause such degradation.Thus, the maximum temperature limit of the filamentary material iseasily exceeded. In addition, the pressure-type extrusion process couldnot be used to jacket a multistrand or bundle of filamentary materialbecause the bundle is not round and would fail to seal the outlet of thefilament guide within the extruder which results in leakage of theextrudable material back into the filament guide.

In a tubing-type extrusion process, the major problem faced is that onextrusion of the plastic tube, the inner diameter of the plastic tube islarger than the outer diameter of the filamentary material which resultsin a loose fit. It is important that the filaments be held firmly ateach end of the lightguide for efficient pick-up and display of light.Lightguides prepared using a loose jacket require that the ends bespecially treated by potting or clamping to immobilize the ends. Thisproblem can be partially solved by stretching the tubing while it isbeing drawn down around the filamentary material, but this createsstresses in the tubing which cannot be relieved on a production linebasis due to the low heat tolerance of the plastic filamentary material.Due to these stresses, the tubing or jacket may later shrink whensubjected to in-service temperatures leaving the filamentary materialexposed and possibly yielding a kinked lightguide. An additional problemis that the tubing, when stretched, takes the shape of the bundle whichmay vary from oval. to round or from flat to square. The resultantcrosssectional irregularity of the lightguide causes great difiiculty inprocessing through automatic cutting machines and machines used forcrimping fittings onto the lightguide.

The process of this invention provides a continuous plastic jacketedplastic optical lightguide of high quality in which the bundle ofplastic optical filaments is held tightly together in a round protectivejacket.

This invention is a process for jacketing polymeric optical filaments toproduce a protectively jacketed lightguide product of substantiallyuniform diameter comprising the steps of extruding a jacketing materialthrough a die orifice having a land up to 20 mils in length from anannular section of a melt reservoir defined by a melt; chamber and theexterior surface of a filament guide to form a tube, the filament guideterminating spaced from said orifice and within the reservoir, the outerdiameter of said tube being formed on the die orifice, andsimultaneously within said tube and while said tube is forming passingone or more polymeric optical filaments through the filament guide, andpassing gas through said filament guide to cool the optical filaments insaid guide, and prior to passing said optical filaments through saidguide adjusting the spacing between the end of said filament guide andsaid orifice an amount defined by a Y factor of 640% where [(bundleO.D.-tubing 1.1). bundle 0.1). 1

whereby in the space defined by the die orifice and the terminus of thefilament guide jacketing material passes about and is in intimatecontact with said optical filaments; and passing said jacketedlightguides through said die to form a uniform outside diameter on saidjacketed lightguides. Preferably, Y is between 15-28% and the polymericoptical filaments are in the form of a substantially untwisted bundle.

This invention also comprises apparatus for protectively jacketingoptical filaments of a first polymeric material With a second polymericmaterial whereby the first material is exposed for only short durationto elevated temperature and which protectively jacketed product has asubstantially uniform outside diameter, said apparatus comprising Meansfor introducing said second polymeric material to a melt reservoir,

A melt reservoir,

A die orifice,

A tubular filament guide member, 1

Said melt reservoir containing therein said tubular filament guidemember axially disposed with said reservoir and spaced from said dieorifice,

Said tubular member on the end disposed toward said orifice havingconverging configuration on its exterior surface and the inner walls ofsaid melt reservoir in the region of said orifice forming a convergingsurface, the converging surfaces of said reservoir and said tubularmember forming a converging annular passage for the flow of said secondpolymeric material,

The inner surface of said tubular member disposed to receive opticalfilamentary material from outside said (bundle O.D.tubing I.D.)

Y bundle O.D.

said orifice having a land of from to 20 mils, whereby the secondpolymeric material passing around said tubular member flows aboutpolymeric optical filaments of said first polymeric material in thespace between the end of tubular member and said orifice before beingextruded through said die to form a protectively jacketed light guide ofsubstantially uniform diameter. Preferabl Y is between and 28%.

This and other embodiments of this invention will be hereinafterdescribed with reference to the following numbered drawings:

FIG. 1 shows a schematic end elevation of an extruder cross-head;

FIG. 2 shows an enlarged section of FIG. 1 taken on line 22;

FIG. 3(a) shows an enlarged section of the die and filament guide ofFIG. 2 producing a plastic tubing;

FIG. 3(b) shows the section of the die and filament I guide of FIG. 3(a)as a bundle of plastic optical filaments are being fed through thefilament guide;

FIG. 3(c) shows the section of the die and filament guide of FIG. 3(b)with the buidle of plastic optical filaments completely filling theplastic tubing;

FIG. 4 shows an enlarged cross-section of a bundle of plastic opticalfilaments;

FIG. 5 shows an enlarged cross-section of the finished lightguide ofthis invention in which the bundle of plastic optical filaments arejacketed in a protective plastic jacket.

Referring to the drawings, FIG. 2 shows an extruder cross-head 1including structure defining an extrudate chamber 6, a circular die 4 atone end of the chamber and a tubular filament guide 12 extendinglongitudinally within the chamber. The die 4 has an outer or die face 8and an inner face of a uniformly converging surface 9 which terminatesinto the die face 8 to form an orifice 2. The filament guide 12 hasthreads 19 designed to engage a fixed nut 22 and is adjustable along itslongitudinal axis which intersects the center of orifice 2, by screwingthe filament guide into or out of the fixed nut. The guide can then belocked in place by tightening the locking nut 20 that is separated fromthe fixed nut 22 by a nut spacer 21. Any other conventional filamentguide adjustment means can also be used. The tubular filament guide 12has a filament outlet 14 which communicates with the extrudate chamber 6and is recessed from the die face, a filament inlet 15 whichcommunicates with the atmosphere, and a filament tube 18, whichlongitudinally divides the interior of the filament guide into an innerchamber 17 and a concentric outer chamber 16. The filament tube 18 hasholes 13 therein which allow chambers 16 and 17 to communicate. Chamber16 is connected to a source of suction (not shown) through valve 24 toproduce a vacuum within the inner chamber 17 by withdrawing air fromchamber 16 slightly faster than it can enter chamber 17 through inlet15.

As shown in FIG. 3(a), molten extrudate is received from an extruder(not shown) by extrudate chamber 6, and the extrudate flows around thetapered end of the filament guide 12 and out orifice 2 in the form of atubing 11. The filament guide 12 is longitudinally adjusted within theextrudate chamber so that the outlet is recessed from the die face 8sufficiently to produce an inner diameter of tubing [I.D. in Equation l]which is less than the outer diameter as hereinafter defined of theoptical filamentary material to be packeted with the tubing.

The outer diameter of filamentary material of irregular cross-sectioncan be considered as the outer diameter of an equivalent essentiallycircular area.

The filamentary material in the form of a bundle 10 of optical filamentsis passed through the inner chamber 17 or filament tube 18 of thefilament guide 12 and into the interior of tubing 11 as is shown in FIG.3(b). Upon continuing passage of the bundle 10 through the filament 12and extrusion of the tubing 11, the entire interior of the tubingbecomes occupied with the bundle as shown in FIG. 3(c).

The spacing between the tip of the filament guide and the die orifice isadjusted such that Y as defined by Equation I below is between 6 to 40%and preferably 15 (bundle O.D.tubing LDQ] l: bundle 0.1).

all terms as hereinbefore defined.

The tubing ID. as discussed with relation to FIG. 3(a) is the innerdiameter of a tubing jacket extruded through the equipment at a givenspacing of filament guide to die orifice without the presence of thefilaments to be protectively jacketed.

The vacuum present within the filament guide 12 main-= tains theintimate contact between the bundle 10 and tub-= ing 11 obtained withinthe die as the tubularly jacketed bundle leaves the die 4. The vacuumalso improves penetration of the extrudate melt into the bundle withinthe die to improve the tightness of fit. In addition, the vacuumproduces a cooling effect on the bundle and filament tube 18, bymovement of air through chambers 16 and 17 as above described.

The intimate contact between bundle 10 and tubing 11 obtained within thedie dispenses with the need for any substantial amount of drawing of thetubing after it leaves the die. Thus, stresses are not created in thetubing to the extent that such stresses might later, in service, berelieved, causing kinking of the lightguide and relative move mentbetween optical filaments and tubing (protective jacketing material).

The optical filamentary material to be jacket by the process of thisinvention can be in the form of a single filament or a bundle thereof,i.e., more than one filament running contiguously with one another.Generally, the filaments of the bundle will be untwisted with respect toeach other, resulting in a bundle of irregular cross-section, a factorwhich makes the extrudate melt backwards flow problem particularlyacute, but which is overcome by the process of the present invention.

FIG. 4 shows a cross-section of a bundle 10 of untwisted optic filaments30 which can be passed through the filament guide 12 for jacketingaccording to the present invention. This figure also shows theirregularity of the cross-sectional outline of the bundle.

In FIG. 5, the bundle 10 of FIG. 4 is shown with a tight protectiveplastic jacket of tubing 11 applied accord ing to the present invention.The cross-sectional outline (outer surface) of the tubing is round,despite the irregular outline of the bundle 10. The tubing 11 haspenetrated the bundle 10 rendering its filaments, for practicalpurposes, immobile with respect to one another and to the tubing. Inaddition, the bundle 10 is Well centered within the tubing.

Suitable materials for use in jacketing optical filamentary material bythe process of the present invention are any of those materials whichare extrudable into a tubing under the conditions hereinbefore describedwithout degrading the particular filamentary material. being used as acore and which have a protective quality for the filamentary material.The jacketing material should be non reactive, in the sense that theoptical quality of the filumentary material is adversely effected, withthe optical filamentary material during jacketing and subsequent use-tExamples of suitable jacketing materials include natural and syntheticrubber and a-monoolefin polymers and cpolymers, such as polyethylene,preferably having low or medium density, and polypropylene, and vinylchloride guide outlet recessed from the die face to produce an ex trudedtubing having an inner diameter smaller than the outer diameter of theoptical filamentary material to be jacket. The filament guide waslongitudinally adjusted in polymers and copolymers each containingnon-migraorder to vary the interference fit and jacket thickness toryplasticizers. Then the optical jfilamentary material was passed throughPreferably, the converging surface 9 of the die 4 terthe filament guideand was jacketed with tubing. Details minates at the die face 8, asshown in FIG. 2, in order that of these runs are given in the followingtable. The optical outlet of the filament guide 12 can be positioned asclosely filamentary material. in runs 1-13 is polymethylmetlp aspossible to the die face yet recessed therefrom to pro- 10 acrylatesheathed in a fluoroalkyl methacrylate polymer as duce the fit betweendesired protective jacket'ing tubing 11 described in British Pat. No.1,037,498, and in run 14 and the optical filamentary material. A smallamount of is polystyrene sheathed in polymethylmethacrylate.

TABLE l.MATERlALS Optical filamentary material Jacket material BundleFilament outer No. filudiameter diameter Density Melt Durometer merits(mils) (mils) Material at 23 C. index hardness 16 10 45 Polyvinylchloride A scale, 82. 16 10 45 .do Do. 32 10 1. .1 0 scale, 79. 16 100.917 4.0 16 10 0. 917 4.0 16 10 0.005 4.8 16 10 0.905 1.5 48 10 0.9303.0 64 10 02 do 0. 930 3.0 32 10 65 Polyvinyl chloride 1. A scale, 82.

4 20 47 Polyethylene- 0. 930 8. 0 1 20 20 do'. 0. 030 3.0 1 0. 930 3.016 10 0. 930 4.0

1 Nitrile rubber plasticizer. 2 Polymeric polyester plasticizer.

TABLE II.-CONDITIONS AND RESULTS Filament Melt temp. Linear JacketDiameter guide Die otjacket jacketthickof outlet orifice Inter- Vacuummaterial ing rate ness product size size fercnce (in. of C C.) (f.p.m.)(mils) (mils) (mils) (mils) (mils) Hg) 147 89 20 86 55 86 10 7 150 29620 86 55 86 10 7 167 96 20 110 76 110 14 7. 5 150 50 20 85 55 86 10 7.5152 106 20 86 55 86 10 7. 5 199 97 20 86 55 86 10 6 192 110 20 86 55 8610 7 163 111 20 119 90 120 18 s 159 130 20 130 105 125 20 16. 3 14s 8015 100 76 103 11 10 157 200 20 88 55 86 10 15 181 153 10 30 52 5 7.8 150173 28 86 86 5 16. 2 163 136 20 86 86 10 12. s

land defining orifice 2 may be present between the die face and theconverging surface in order to minimize orifice wear. As this land isincreased, so does back pressure. Consequently, as small a land aspossible should be used in carrying out the process of this invention.Exemplary of the amount of land that can be used is land up to 20 milswide (distance between die face at orifice and converging surface atorifice) which gives an orifice of corresponding length.

The outer diameter of filamentary material or irregular cross-sectioncan be considered as the outer diameter of an equivalent essentiallycircular area.

EXAMPLES A. number of runs were made according to the following generalprocedure: An adjustable filament guide and die designed and fabricatedas above-described were installed in a standard extruder cross-head withthe filament As many apparently widely different embodiments of thisinvention may be made without departing from the spirit of scopethereof, it is to be understood that this invention is not limited tothe specific embodiments there of except as defined in the appendedclaims.

I claim:

1. Process for jacketing polymeric optical filaments to produce aprotectively jacketed lightguide product of substantially uniformdiameter comprising the steps of extruding a jacketing material througha die orifice having a land up to 20 mils in length from an annularsection of a melt reservoir defined by a melt chamber and the exteriorsurface of a filament guide to form a tube, the filament guideterminating spaced from said orifice and within the reservoir, the outerdiameter of said tube being formed on the die orifice, andsimultaneously within said tube and while said tube is forming passingone or more polymeric optical filaments selected from polymethybmethylacrylate sheathed in a fluoroalkyl methacrylate polymer orpolystyrene sheathed in polymethylmethacrylate through the filament'guide, 'and passing gas through guide to cool the optical filaments insaid guide,

and prior to passing said optical filaments through said guide adjustingthe spacing between the end of said filament guide and said orifice anamount defined by a Y factor of 6-40% where FBQW bundle O.D.

whereby in the space defined by the die orifice and the terminus of thefilament guide the jacketing material passes about and is in intimatecontact with said optical filaments; and passing said jacketedlightguides through said die to form a uniform outside diameter on saidjacketed lightguides.

2. Process of claim 1 wherein Y is between 15-28%.

3. Process of claim 1 wherein the polymeric optical filaments are in theform of a substantially untwisted bundle.

References Cited UNITED STATES PATENTS Ingmanson l8--l3 T Churnell etal. 18--13 T Berggren 2- 264--174- Sussenbach 161-176 Lorenian ...m.264--l72 OBrien 264-1 Lorenian 1813 T Raydt et al 264-174 Henning et a1.264-l74 Cohen 264-174 Fyfe 2641 JULIUS FROME, Primary Examiner A. H.KOECKERT, Assistant Examiner US. Cl. X.R.

